1. Field of the Invention
The present invention relates to a recording head with a temperature sensor, and a printer with the recording head.
2. Description of the Prior Arts
As a printer for recording an image on a recording material by using a recording head, widely known is a color direct thermal printer to make a full-color print on a color thermal recording paper in which thermosensitive coloring layers developing cyan, magenta and yellow colors are overlaid on a support one by one. In the color direct thermal printer, three-color images are recorded in frame-sequential fashion by a thermal head while the color thermal recording paper is fed. The thermal head is provided with a heating element array in which plural heating elements are arranged linearly.
In prior art color thermal printers, driving energy to the heating elements is adjusted in accordance with head temperature measured by a temperature sensor attached to a head substrate of the thermal head, in order to prevent density unevenness caused by accumulation of heat in the heating elements.
The driving energy is preferably corrected based on temperature near the heating element array. However, in prior art thermal heads, the temperature sensor is attached to the head substrate, and the heating energy from the heating element array is transmitted to the temperature sensor through the head substrate and an element substrate having plural driver ICs for driving the heating element selectively. Therefore, there has been a problem that the temperature measured by the temperature sensor is different from the actual temperature near the heating element array.
In order to solve the above problem, in a thermal line printer described in U.S. Pat. No. 2,627,348 estimates the temperature near the heating element array based on arithmetic expressions using the measurement result of the temperature sensor.
However, in the above thermal line printer, much calculation is required to estimate the temperature near the heating element array, and, it is necessary to provide an arithmetic circuit for such calculation. This results in requiring a certain amount of time for the arithmetic processing, and to make matters worse, increasing the manufacturing cost. In addition, it is difficult to obtain parameters for the arithmetic expressions which contribute to prevent the density unevenness.
There are various techniques for mounting the temperature sensor. For example, the thermal printer described in Japanese Patent Laid-Open Publications No. 62-170366 has a thermistor, as the temperature sensor, in the rear surface of a ceramic substrate as the element substrate. However, any concrete wiring methods are not mentioned, and this technique is somewhat impractical.
In a thermal head in Japanese Published Examined Application No. 4-17798, the thermistor is disposed around a driver IC array in the ceramic substrate. However, the thermistor cannot be attached near the heating element because the platen roller would interfere with the thermistor. Additionally, if the plural thermistors are attached in the main scanning direction, some space should be made to attach them around the driver IC array. Thus, there is a problem that the size of the thermal head becomes unnecessarily large in the main scanning direction.
In the thermal head described in U.S. Pat. No. 3,389,419, the thermistor and the driver IC are put in a concave portion formed in the ceramic substrate. This configuration prevents the platen roller from interfering with the thermistor but the concave portion is hard to form in the element substrate, so that the manufacturing cost is increased. In addition, the problem about the size of thermal head in Japanese Patent Laid-Open Publications No. 4-17798 cannot be solved.